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Instrument on Mars Rover 'Spirit' Malfunctioning
deglr6328 writes "During the first in-flight checkout of both mars rovers this week it was found that the Mossbauer spectrometer on the first launched "Spirit" Rover was not functioning properly. The instrument is intended to be used on the surface of Mars to examine the composition and magnetic properties of Iron containing minerals in rocks. Mission engineers think they may be able to partially fix the spectrometer before it arrives in January. All other cameras and instruments on both rovers checked out ok."
I'm not sure exactly how they plan to fix the spectrometer but I'm sure they're not lying when they say it's an option. Remember the Galileo space probe was recently fixed from hundreds of millions of miles away. Since a Mossbauer spectrometer uses a moving radioactive source to take a spectrum I would guess it might be put through it's paces several times to try to work out a glitch(speculation). The Japanese Mars probe with a failing circuit breaker is currently undergoing repairs to fix it remotely too.
- "Hear that?! The percolations are imminent! Cease your ingress!"
Note: I work on the Mars Exploration Rovers mission, developing Ground Data Systems software used by the scientists. I'm also completing a degree in Physics.
I'm not sure exactly how they plan to fix the spectrometer but I'm sure they're not lying when they say it's an option. Remember the Galileo space probe was recently fixed from hundreds of millions of miles away. Since a Mossbauer spectrometer uses a moving radioactive source to take a spectrum I would guess it might be put through it's paces several times to try to work out a glitch(speculation).
It's really quite amazing what can be fixed remotely, or at least worked around... If there's a significant mechanical problem with the instrument, however, there's not that much that can be done. From what I've heard, the Mossbauer on Spirit isn't currently getting data at full resolution, but they may be able to compensate for that by reprogramming the instrument remotely.
In case you don't already know, the Mossbauer spectrometer is a rediculously cool instrument. The way it works is the following:
According to elementary quantum physics, the energy levels of the nucleus are preturbed by the presence of nearby magnetic fields. Because electrons are charged fermions (and thus have nonzero spin), they have a dipolar magnetic field which can interact with the nucleus via hyperfine splitting. Hyperfine splitting is the creation of two or more distinct energy states from a single energy state via spin coupling. As an example, imagine a bar magnet which is held at the top of a one-foot drop. It has a very specific potential energy (in quantum physics energy is quantized and thus exists only in discrete amounts). Now, imagine that a uniform magnetic field is turned on in the lab room, pointing along the Z-axis (up/down). The bar magnet, if allowed to rotate, will want to minimize its energy by aligning itself antiparallel to the magnetic field (remember, opposites attract). To twist it into the "parallel" orientation, energy must be exerted, thus the single energy level of the bar magnet is now two distinct energies (in the quantum case, the difference between energy levels caused by hyperfine splitting is very small, hence the term "hyperfine"). This is a rough analogy to what's going on in the nucleus. Still with me? Good!
Now, what does this have to do with the spectrometer? Well one of the most important pieces of information we can gather about rocks on Mars is their chemical composition. Most people are aware that Mars' rusty color is due to the high concentration of iron oxides on the surface. From high school chemistry we can remember that metals have multiple valence numbers they can use to bond with other atoms... It turns out that the electron configuration of the different bonds causes the electric and magnetic field from the electrons to vary significantly.... And if the magnetic field is varied, so is the hyperfine splitting! So... the nucleus itself is slightly affected by the valence shell geometry, among other things.
So, how do we detect these differences in hyperfine splitting? That's where the Mossbauer spectrometer comes into play. The spectrometer contains two pieces of raioactive cobalt-57 (each about the size of a pencil eraser) as sources of gamma-radiation quanta. The cobalt-57 decays into an isotope of Iron with an excited nucleus. The excited nucleus quickly decays, emitting the exact gamma-quanta required to excite another iron nucleus. This gamma radiation exits the instrument and strikes a rock. Inside the rock iron nuclei absorb and re-emit the gamma radiation to be detected by the spectrometer.
The variations in the energy levels in the iron in different chemical forms are just large enough that the addition of a dopplar shift to the radiation source allows us to detect it reliably. The radiation source slides towards and away from the target at specifically varying speeds, and because the gamma rays energy levels are changed slightly by the dopplar